I saw a post about this somewhere else, but I think I'll just follow up here since the questions haven't been asked yet - how long has your lavender bush been around for? Have you done anything differently to change how the bush is being cared for that could have affected how it's doing? You may want to take note of any major changes in the weather too to see if that could have been the cause too. As mentioned, bees may not be your solution.

I should think that you would want to examine what you're currently doing with the lavender bush first as what abwal is suggesting here. Could be a number of different factors - did you change anything about the way you've been caring for it recently that could have caused the change? Is it a new bush or has it been around for long? Perhaps it's getting too much sun all of a sudden too. A lot of factors at play mate.